Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.91   3.638%   $58.9804   $58.98   $59.00   $59.00  
  Purchase #2 $97.32   5.135%   $102.3174   $102.32   $102.30   $102.30  
  Purchase #3 $76.37   7.496%   $82.0947   $82.09   $82.10   $82.10  
  Purchase #4 $226.73   11.676%   $253.203   $253.20   $253.20   $253.20  
  Purchase #5 $137.31   11.284%   $152.8041   $152.80   $152.80   $152.80  
  Purchase #6 $85.54   9.616%   $93.7655   $93.77   $93.75   $93.80  
  Purchase #7 $141.81   7.364%   $152.2529   $152.25   $152.25   $152.30  
  7 purchase totals = $821.99       $895.4180   $895.41   $895.40   $895.50